Electro-pneumatic process controller



Aug. 16, 1966 K. G. KREUTER 3,266,379

ELECTRO-PNEUMATIC PROCESS CONTROLLER Filed Dec. 19, 1965 4 Sheets-Sheetl INVENTOR Kennei'h G. Kramer BY mwz M 75m ATTORNEYS Aug. 16, 1966- K.G. KREUTER ELECTED-PNEUMATIC PROCESS CONTROLLER 4 SheetsSheet 2 FiledDec. 19, 1963 ATTORNEYS g- 1 56 K. G. KREUTER ELECTRO-PNEUMATIC PROCESSCONTROLLER' 4 Sheefs-Sheet 5 Filed Dec." 19, 1963 FIG. 4.

INVENTOR Kenneth G. Kreuter BY M ATTORNEYS Aug. 16, 1966 G. KREUTERELECTRO-PNEUMATIC PROCESS CONTROLLER 4 Sheets-Sheet Filed Dec. 19, 1963[MENTOR Kenneth G.Kreuter.

BY M

ATTORNEYS United States Patent 3,266,379 ELECTRO-PNEUMATIC PROCESSCONTROLLER Kenneth G. Kreuter, Goshen, Ind, assignor to RobertshawControls Company, Richmond, Va., a corporation of Delaware Filed Dec.19, 1963, Ser. No. 331,968 13 Claims. (Cl. 91-374) This invention is acontinuation-in-part of my copending patent application Serial No.282,936, filed May 24, 1963, now Patent Number 3,216,331.

This invention relates generally to process controllers utilizingelectro-pneumatic converters and more particularly, means for convertinga duration modulated binary electric signal into a pneumatic controlsignal which ultimately positions, pneumatically, a control means suchas the valve stem of a process control valve.

In dynamic control systems such as process controls having integralcomputer means as the brain or monitor thereof, it is often necessary toconvert electric output signals from the computer into a functionallyrelated class of signals such as pressure and/ or displacement.

It is an object of this invention to provide a process control system orthe like for first performing an electropneumatic conversion andsubsequently converting the resulting pneumatic signal into adisplacement functionally related to both the electric and the pneumaticsignals in the system.

It is another object of this invention to provide a process controlsystem or the like wherein a duration-modulated binary electric outputsignal from a digital computer or the like is first converted to acontrol pressure and that control pressure is subsequently converted toa displace ment, the displacement being imposed on a movable controlmeans.

Still another object of this invention is to provide a process controlsystem or the like wherein a durationmodulated binary electric outputsignal from a digital computer or the like is first converted to acontrol pressure and that control pressure is subsequently converted toa displacement, the displacement being imposed on a movable controlmeans, said system including a novel intercoupled input drive anddisplacement feedback means whereby said system is highly stable.

Yet another object of this invention is to provide a system forpneumatically positioning a control valve or other displaceable controlmeans in response to a duration-modulated multiple-state electricsignal.

A further object of this invention is to provide systems forpneumatically positioning a control valve or other dis-placeable controlmeans in response to a multiple-state electric signal and effect acontinuous remote readout of the position of the said control means.

Yet a further object of this invention it to provide systems forpneumatically positioning a control valve or other displaceable controlmeans in response to multiplestate electric signals, said systems havingnovel throttling means therein for selectively varying the response ofsaid systems to said multiple-state electric signals.

These and other objects of the invention will become more fully apparentwith reference to the following specification and drawings which relateto several preferred embodiments of the invention.

In the drawings:

FIGURE 1 is a schematic of one embodiment of the system of the presentinvention with the novel structural components thereof shownisometrically;

FIGURE 2 is a schematic of another embodiment of the system of thepresent invention with the novel structural components thereof shownisometrically;

FIGURE 3 is a schematic pneumatic flow diagram illustrating anotherembodiment of the invention applicable to either of the systems ofFIGURES 1 and 2;

FIGURE 4 is a side elevation of yet another embodiment of the invention,in cross-section, with the novel structural components thereof shown ina final packaged assembly;

FIGURE 5 is a detail of the pneumatic leakport assembly of FIGURE 4;

FIGURE 6 is a cross-sectional detail of the novel throttling means takenalong line 66 of FIGURE 4;

FIGURE 7 is a detailed isometric of the throttling valve spool of FIGURE4;

FIGURE 8 is a schematic gear diagram of the feedback and monitoringgearing of the embodiment of FIG- URE 4; and

FIGURE 9 is an isometric of the fully assembled en cased embodiment ofFIGURE 4.

Referring in detail to the drawings, and more particularly to FIGURE 2,the embodiment of the invention shown therein will now be described.

The electrical input source 10 comprises first and second relay switches12 and 14, respectively, representatiive of the two different states ofa binary signal. The coils of the relay switches 12 and 14 areselectively energized by the binary output signal of a digital computer16, generally shown in block diagram form as having two output leads 1and 0 represent the binary output states of the said computer 16. Thecomputer senses variations in the parameters of a process or the likewhich is being controlled by the present invention.

The relay switches 12 and 14 are connected with a common terminal 18, towhich is connected a first power lead P A second power line Prepresenting the other side of a suitable power supply 20, is directlyconnected to the common or neutral input terminal 22 of a reversibleelectric servo-motor 24.

The first relay switch 12 is connected to respond to a zero state outputfrom the computer terminal 0 and is provided with a terminal contact 26connected, via a lead 28, to an input terminal 30 on the servo-motor 24which, when energized, causes the said motor to rotate in acounter-clockwise direction.

The second relay switch 14 is connected to respond to a unit stateoutput from the computer terminal 1 and is provided with a contactterminal 32 connected, via a lead 34, to an input terminal 36 on theservo-motor 24, which, when energized, causes the said motor to rotatein a clockwise direction.

The servo-motor 24 comprises the motive means of an electro-pneumatictransducer generally indicated by the numeral 38.

The transducer 38 further includes the rotary output shaft 40 of theservo-motor 24, a manual override disk or wheel 42, integrally andcoaxially mounted on the shaft 40, a cylindrical hub 44 integral withthe wheel 42 and extending outwardly and coaXially therefrom, and aninput or control cam 46 integrally mounted on the outer end of the hub44 and adapted, along with the wheel 42 and hub 44 to rotate with and onthe axis of the motor shaft 42. The above-defined combination ofelements provides a mechanical displacement input to theelectropneumatic transducer 38 as a function of the electric signalinput to the servo-motor 24 as will be hereinafter more fully described.

A control follower 48 is provided for the control cam 46 in the form ofa bifurcated elongated lever pivoted at its unitary end 50 to a suitablefixed pivot means 52. One leg of the bifurcated portion of the controlfollower 48 is engaged with the periphery 54 of the control cam 46, thesaid periphery 54 comprising the cam contour of the said control cam. Anadjustable cam indexing means is provided in the form of a threaded camindexing detent 56 which screws in and out of a fixed mount 58positioned by any suitable means adjacent the periphery 54 of thecontrol cam 46. The indexing detent 56 is adapted to engage the fallsurface 60 on the peripheral cam contour 54 of the said control cam.

A leakport nozzle 62 having a leakport 64 in the tip thereof is mountedon the outer tip of an integral laterally extending arm 66 on athrottling range slide means 68 adjustably and slidab'ly mounted forlongitudinal adjustment on the bifurcated portion of the controlfollower 48, via a throttling range set-screw 70.

The leakport nozzle 62 is supplied with pneumatic pressure by means of apressure hose 72 communicating with the pilot or signal chamber 74 of astacked multiple diaphragm type pneumatic relay 76. The pilot pressurein the pilot chamber 74 is derived from the main air supply chamber 78of the relay 76 via a bleed port 80 having an in-line flow re's-trictor82 therein.

The main air chamber 78 is supplied by a suitable pressure source 84 andis connected with the output chamber 86 of the relay 76, known in theart as either the branch or control pressure chamber, by the lower halfof a twoway relay poppet 88 seating internally of the main air chamber78.

The upper end of the poppet 88 seats within the output chamber 86 on adiaphragm carried floating valve seat 90, whereby the output chamber 86is controllably interconnected with the exhaust chamber 92. The valveseat 90 is part of a spacer structure 94 which separates and remainsmobile with the two diaphragms 96 and 98 which, combined with theinternal cavity of the relay 76, define the pilot, output and exhaustchambers 74, 86 and 92, respectively.

The exhaust chamber 92 is connected with the atmosphere via a vent port100. The branch pressure or output chamber is delivered to any device tobe controlled thereby via an output port 102.

The output port 102 is connected to the topwork of a pneumaticallypositioned valve, as will be hereinafter more fully described withrespect to FIGURE 3, the valve not being shown in FIGURE 1.

The valve stem 104 is displaceable in response to various values ofbranch pressure from the relay 76, and this displacement is utilized asthe input signal for the feedback mechanism 106 of the electro-pneumatictransducer 38.

An integral lateral extension 108, shown here as a flat radial lever, isprovided on the valve stem 104. One end of a flexible link such as aball chain or cable 110 is affixed to the extension 108, the other endand several convolutions thereof being wound on a rotatably mountedstorage drum 112. Thus, the drum 112 is adapted to be rotated by thechain-110 in response to a displacement of the valve stem 104.

The drum 112 is integrally and coaxially mounted for rotation with arotary shaft 114 which in turn drives an integrally and concentricallymounted first pinion gear means 116. The first gear 116 is intermeshedwith and adapted to drive a second pinion gear means 118, the saidsecond gear means being integrally and concentrically mounted on one endof a shaft 120.

A feedback cam means 122 is integrally mounted on the other end of theshaft and is adapted to rotate therewith. The feedback cam contourcomprises the periphery 124 of the feedback cam and includes a fast fallsurface 126.

The cam shaft 120, the feedback cam 122, the control cam 46 and theservo-motor shaft 40 are mutually coaxial. The opposed end faces of thecontrol and feedback cams 46 and 122, respectively, are interconnectedby way of torsion spring means 128 anchored at each of its ends to oneof the said end faces and coaxially disposed with respect to the saidcams.

Mounted immediately adjacent the periphery 124 of the feedback cam 122is an elongated feedback or leakport lever 130, pivoted at one end to apivot means 132, co-

axial with the pivot means 52 of the control follower, and extending toa position whereby the surface of the said leakport lever is engageablewith the leakport 64 at a point adjacent the other end thereof.

A vertically adjustable threaded detent 134 extends through the leakportlever into engagement with the periphery 124 of the feedback cam 122 andthus, comprises an adjustable cam follower for varying the verticalposition of the leakport lever 130 as a function of the angular positionof the feedback cam 122, and hence, the position of the valve stem 104.

A zero stop for the feedback cam 122 in the form of a fixed detent 136is positioned adjacent the periphery 124 of the said cam and is adaptedto engage the fast fall surface 126 when the cam is in the predeterminedzero position.

Referring now to FIGURE 2, a second embodiment of the invention will nowbe described, like parts to FIG- URE 1 bear the same numerals.

The ele'ctro-pneumatic transducer generally indicated at 138 is shown asincluding a first input pinion 140 is concentrically and integrallymounted on the servo-motor shaft 40. The first input pinion 140 isintermeshed with and adapted to drive a second input pinion 142, thesaid second pinion being an integral ofiset concentric portion of arotary leakport positioning disk assembly 144. The assembly 144 alsoserves as a manual override device.

An integral shelf 146 is provided adjacent the periphery of the diskassembly 144 and on that face of the said disk assembly 144 removed fromthe second input pinion 142. The shelf 146 is adapted to threadablyreceive a throttling range screw 148 therein which acts as a positioningand hold-down means for one end of a flat control lever 150 extendingoutwardly from the shelf 146 in a plane perpendicular to the face of thedisk assembly 144.

A leakport nozzle 152 is mounted through the control lever 150 adjacentthe free end thereof with the leakport 154 therein opening upward asshown. The leakport nozzle 152 is supplied with pressure from the relay76, already described with reference to FIGURE 1, via a pressure line ortube 156.

The feedback mechanism 158 of the embodiment of FIGURE 2 is identical tothat of FIGURE 1 as to the valve stem 104, integral extension 108, chain110, drum 112, drum shaft 114, first feedback pinion 116, secondfeedback pinion 118 and the rotary shaft 120.

The end of the shaft 120 removed from the second feedback pinion 118mounts an integral concentric leakport lever control disc assembly 160.The control disc assembly 160 includes a longitudinally extending stoppin 162 which is radially offset with respect to the axis of rotation ofthe rotary shaft 120 and control disk assembly 160.

The control disk assembly 160 and the positioning disk assembly 144 .arecoaxially disposed. 'I he opposing faces of the said disc assemblies areresiliently coupled together by first and second axially disposedtorsion springs 164 and 166, respectively, the said springs being spacedapart at their respectively adjacent end portions by an axially disposedspacer means 168. The other end of the first torsion spring 164 issuitably anchored to the face of the positioning disk assembly 144 andthe other end of the second torsion spring 166 is suitably anchored tothe face of the control disk assembly 160.

As shown, the spacer 168 is of a cylindrical shape and in combinationwith the torsion springs 164 and 166 comprises a biased pivotal mountingfor the leakport lever 170, which extends radially outward from thespacer 168 to a position above and adjacent the leakport 154.

Referring now to FIGURE 3, the flow diagram into and out of the relay76, excluding the leakport connections thereto, is shown with a manualcontrol valve 172 which is adapted to selectively bypass the relay 76and connect the main air supply 84 directly with the valve top work 174via a pressure line 176.

The valve top work 1 74 is shown as comprising a cylinder 178, a piston180 reciprocable in said cylinder and a diaphragm 182 defining anexpansible chamber "184 between the upper end of the piston 180 and thecylinder 178.

The chamber 184 is directly supplied by the pressure line 176.

The valve stem 104 is axially and integrally connected with the piston180 for reciprocation therewith.

The main air supply 84 is connected with the valve 172 via a supply line186. The valve 172 is connected to the input or main air inlet of therelay 76 via an input line 188 and the branch pressure output port 102of the said relay is connected back through the valve 172 via an outputline 190. When the relay is connected in the pneumatic circuit, the mainair line 186 is connected through the valve 172 with the relay inputline 188 and the relay output line 190 is connected with the chamber 184in the valve top work 174 via the manual valve 172 and the line 176.

Operation Referring again to FIGURE 1, the operation of the embodimentshown therein will now be described.

' A condition for all of the foregoing embodiments is that the outputs 1and from the computer 16 are duration modulated as a function of thesensed variations in process parameters, such that either the relayswitch 12 or the relay switch 14 in the system input means 10 will beenergized for various periods of time. This results in a selectivecompletion of either a first motor circuit comprising power lead Pcommon terminal 18, contact 26, line 28, motor terminal 30, common motorterminal 22 and power lead P or a second motor circuit comprising powerlead P common terminal 18, contact 32, lead 34, motor terminal 36,common motor terminal 22 and power lead P The said first circuitenergizes 22 and power lead P The said first circuit energizes theservo-motor 24 for counter-clockwise rotation for the duration of a zerostate output signal from the 0 terminal of the computer 16 while thesaid second circuit energizes the servo motor 24 for clockwise rotationfor the duration of a unit state output signal from the 1 terminal ofthe computer 16.

Referring specifically to FIGURE 1, and assuming a clockwise rotation ofthe output shaft 40 of the servo motor 24, the manual override wheel 42,hub 44 and leakport control cam 46 are all rotated in a clockwisedirection for the duration of the unit state signal from the computer16, after which the relay switch 14 will open and de-energize the servomotor 24.

On clockwise rotation, the control cam 46 raises the control follower 48and consequently, the leakport 64 via the combination of throttlingrange slide 68 and leakport supporting arm 66; Thus, instantaneously,the leakport 64 is moved away from the leakport lever 130 permitting agreater flow therethrough to atmosphere. This results in a decrease inthe .pilot pressure in the pilot chamber 74 of the relay76 since thesaid pilot chamber is supplied at a constant rate of flow via thepressure port 80 and in line rest-rictor 82, the variable being theexhaust flow via the pressure tube 72 and leakport 64.

The reduction in pressure causes the spacer assembly 94 and diaphragms96 and 98 to move upward in response to the force diiferential betweenthe branch and pilot chambers 86 and 74, respectively, whereby thefloating seat 90 is raised from the upper end of the relay poppet 88 andthe branch pressure begins to exhaust to atmosphere via the exhaustchamber 92 and exhaust port 100.

Thus, referring now to FIGURE 3 in the condition illustrated therein,the exhaust of branch pressure from the branch pressure chamber 86, viathe output port 102, output line 190, valve 172 and line 176, alsobegins an exhaust of the pressure in the expansible chamber 184 of thevalve top Work 174.

Assuming that the piston 180 is conventionally biased to move into thecylinder 176, such as by a compression spring SP coaxial with the valvestem 104, a reduction of pressure in the chamber 184 will result in adecreased force opposing the piston 180 and the piston 180 and valvestem 104 will move upwardly relative to the positions shown in FIGURES land 3 in response to the said decrease in branch pressure and the forceexerted thereon by the compression spring SP.

This causes the integral extension 108, see FIGURE 1, on the valve stem104 to follow the stem 104 in its upward displacement and tend toslacken the chain 110.

The torsion spring 12-8 has already been constrained to store energy bythe clockwise rotation of the control cam 46 and thus, via the feedbackcam, second feedback pinion, first feedback pinion and drum shaft 114 tobias the drum 112 to rotate in a counter-clockwise direction.

The feedback chain is wound on the drum 1-12 to be taken up thereby inthe biased direction of rotation thereof. Thus, an upward displacementof the valve stem 104 causes the chain 110 to tend to slacken and betaken up by the drum 112 which rotates through an angle directlyproportional to the said displacement. This permits the feedback cam122, via the drum shaft 114, first and second feedback pinions 118 and116 and rotary shaft 120 to follow the control cam in clockwise rotationin an amount proportional to the displacement of the valve stem 104. Theresult is to constrain the leakport lever to follow the upwarddisplacement of the leakport 64 via the feedback cam contour 124 andfeedback cam follower 134 to decrease the leakport flow and tend tobalance the entire system by creating an increase in pressure in thepilot chamber 74 of the relay 76.

The valve stem 104 will continue to be displaced until the pilotpressure decrease imposed on the system via the signal input to theservo motor 24 has been completely nullified by the action of thefeedback means 106 constraining the leakport lever 130 to follow theleakport 64 until the flow therethrough has been modulated to adecreased value sufiicient to restore the initial value of pilotpressure in the pilot chamber 74 of the relay 76.

The restoration of initial pilot pressure eliminates the differentialbetween the branch and pilot chambers 86 and 74, respectively, and thefloating valve seat 90 is reseated on the relay poppet 88, holding thebranch pressure at its resulting lower controlled value and balancingthe relay. The valve stem 104 and its associated process control valvemeans (not shown) have now fully responded to the constraint imposed onthe system by the output signal from the computer 16 and have beendisplaced in an amount having a preselected functional relationship tothe state and duration of the said computer output signal.

Referring now to FIGURE 2, and assuming the same clockwise rotation ofthe motor shaft 40 and the other conditions assumed for FIGURE 1, thefirst input pinion is rotated clockwise with the shaft 40 and drives theleakport positioning disk assembly 144 in a counterclockwise directionvia the second input pinion 142.

As a result, the leakport 154 is moved through the same angle ofrotation as the motor shaft 40 in a peripheral are determined by theposition of the control lever on the integral shelf 146 of thepositioning assembly 144.

This displacement of the leakport 154 is away from the leakport leverwhich, instantaneously, remains in a fixed position, resulting in anincreased flow through the leakport and a resulting drop in pilotpressure in the pneumatic relay 76.

As previously described with respect to FIGURES 1 and 3, and referringnow additionally to FIGURE 3, the drop in pilot pressure causes adecrease in branch pressure which is transmitted from the relay outputport 102 7 to the expansible chamber 184 of the process control valvetop work 174 via pressure line 17%, valve 172 and pressure line 176. Theresulting effect, as previously described, is to cause the piston 180and the integral process control valve stem 164 to be displaced upwardwith respect to the position shown in FIGURES 2 and 3.

Initially, because of the torsion spring coupling comprising the firstand second torsion springs 164 and 166, respectively, and the axialinterconnecting spacer 168 therebetween, the leakport lever 170 isbiased to follow the leakport 154. However, the stop pin 162 on thecontrol disk assembly 16!) engages the lower surface of and imposes aconstraint on the leakport lever 170, via the feedback mechanism 158,whereby the leakport lever 170 only follows the leakport 154 at a rateand through an angular displacement, respectively, proportional to therate of displacement and displacement of the process control valve stem104. The upward displacement of the valve stem 104 permits the chain110-, via the extension 108, to tend to slacken. The bias of the torsionsprings 164 and 166 cause the control disk assembly 161 to rotatecounter-clockwise, whereby, via the shaft 121), the second feedbackpinion 118 rotates counter-clockwise, the first feedback pinion 116 isdriven clockwise and the drum shaft 114 and drum 112 rotate clockwisewith the said first feedback pinion 116 to take up the slack in thechain.

The leakport lever 17% will rotate toward the leakport 154 and the pilotpressure in the relay 76 will thus be continuously modulated toward afinal increased value which will balance the relay '76 when the valvestem 104 has reached a final position in satisfaction of the constraintimposed on the entire system by the duration-modulated input from thecomputer 16 to the servo-motor 24.

The continuous modulation of pilot pressure in both the embodiments ofFIGURES 1 and 2 prevents overshoot of the valve Stern 1194 with respectto the desired displacement imposed thereon by the input signal. Thesystem, in both embodiments is thereby rendered highly stable.

The throttling range or operating range of the system is controlled, inthe embodiment of FIGURE 1, by longitudinally displacing the range slide68 along the bifurcated section of the control follower 48. This movesthe leakport 64 longitudinally of the leakport lever 1311, whereby therelative angular displacement of the leakport 64 and leakport lever 130is selectively varied, producing a corresponding variation in the rangeof flow rates and resulting pilot pressure which can be effected.

In the embodiment of FIGURE 2, the leakport 154 is movable radially withrespect to the axis of rotation of the control disk assembly 160, viathe pivoted control lever 151i, whereby the relative angulardisplacement be tween the leakport 154 and the leakport lever 170 toeffect a variation in the throttling range as described above withrespect to FIGURE 1.

In case of electric power failure or malfunction, both the embodimentsof FIGURES 1 and 2 .are provided with manual override means for placinginput constraints on the system. Rotation of the manual override disk 42of FIGURE 1 or the positioner disk assembly 144 of FIG- URE 2 will causethe same resulting control of the valve stem 1114 as is provided by therotation of the motor shaft 40 of the servo-motor 24.

Referring now to FIGURE 4, this embodiment will now be described withthe several like parts to the embodiment of FIGURE 2 bearing likenumerals.

The servo-motor 24 is energized as described with reference to FIGURE 2and is enclosed in an internal cavity 200 in a housing means 202. Thehousing means 202 contains or supports all of the components of thecontrol system with the exception of the valve stem 104.

The feedback mechanism 153 of the embodiment of FIGURE 4 is identicalwith that of FIGURES 1 and 2 as to the valve stem 104, integralextension 1%, chain 110, drum 112, drum shaft 114, first feedback pinion116, second feedback pinion 118 and the rotary shaft 8 129 of the saidsecond feedback pinion 118. All of the feedback pinions are housed andjournalled in a second internal cavity 203 in the housing means 2112.

Referring additionally to FIGURE '7 the end of the shaft removed fromthe second feedback pinion 118 mounts an integral coaxially extendingvalve spindle 204 which is slidably and rotatably mounted within aconcentric bore 206 disposed beneath the internal cavity 209 in thehousing means 202. A radially offset longitudinally extending stop means208 is provided on the outer end of the valve spindle 204.

Referring to FIGURES 4, 5, 6 and 7, a positioning disc assembly 210 isprovided at the other side of the housing means 202 from the feedbackassembly 158 in a third internal cavity 212. The positioning discassembly 211) includes a pinion gear 214, coaxial with the valve spindle204, driven by the drive pinion 1441 on the output shaft 40 of the servomotor 24 and a leakport positioning disk 216 integral with the innerface of the pinion gear 214 and coaxial therewith. A leakport nozzle 218is provided on the face of the positioning disk 216 which extends towardthe throttling valve spindle 204 radially offset but parallel to theaxis of rotation thereof. The leakport 2211 in the leakport nozzle 218is directed tangentially of the leakport positioning disk 216.

The positioning disk assembly is mounted for rotation with a supportingshaft 222 which is journalled on one end in a bearing 224 in the sidewall of the third internal cavity 212. The other end of the supportingshaft 222 comprises a cylindrical throttling valve head 226 having itsend face 228 formed from a cylinder cut on a forty-' five degree biaswith respect to the axis of the said supporting shaft 222. An O-ring2311 serves as a journal bearing and seal to maintain the valve head 226in proper alignment in the internal bore 232 of the throttling valvespool 204 into which it is telescopically received.

The throttling valve spindle 2-04 is journalled within the bore 206 bymeans of a plurality of axially spaced 0- rings 234 seated in radiallyextending integral shoulders 236 on the said spindle. The bore 2136contains a radially symmetrical constriction 238 which passes thefeedback shaft 120 and acts as an index stop for a coiled compressionspring 246 concentric with the feedback shaft 120. The other end of thefeedback shaft 12%, adjacent the second feedback pinion 118 passesthrough a journal bearing 242 which acts as the other limit stop for thecompression spring 240.

The second feedback pinion 118 is slidably meshed with the firstfeedback pinion 116 and the journal bearing 242 is slidably mounted inthe internal valve bore 2116. A thrust bearing comprising a throttlingscrew 244 is threaded through the side wall of the first internal cavity203 into engagement with a thrust pad 246 at the axis of the secondfeedback pinion 118 on the outer end face thereof. Thus, thesecondfeedback pinion 118, the journal bearing 242, feedback shaft 1211'and valve spool 204 are all adapted to be adjustably positioned againstthe action of the compression spring 240 by means of the throttlingscrew 244.

A leakport lever 248 is provided which has a spring U-clip portion 259at one end frictionally engaging the supporting shaft 222 of thepositioning disk assembly 210, the other end of the said leakport leverextending substantially radially of the positioning disk 216 intoproximity with the leakport 220. The leakport lever 248 is biasedagainst the leakport nozzle by a coiled torsion spring 252 concentricwith the supporting shaft 222, which has one end 254 anchored in theface of the positioning disk 216 while the other end 256 is engaged witha detent 258 in the outer tip of the leakport lever 248.

Means for providing a remote indicationof the position of the feedbackshaft 120 comprises a third pinion gear 260, shown in FIGURES 4 and 8,journalled via a shaft 262 in a bearing 264 in the inner wall of thesecond housing cavity 203. The shaft 262 is connected with a rotarytransducer 266 such as a potentiometer or three terminal resistancewhich provides an electric signal as a function of rotational position.The third pinion 260 is interrneshed with the first feedback pinion 116and is driven thereby in the same manner as the second feedback pinion118 and its associated feedback shaft 120. As shown, the said second andthird pinions are identical such that the gear shaft 262 and thetransducer 226 are rotated in a 1:1 ratio with the feedback shaft 120.

As in the embodiments of FIGURES 1 and 2, a pneumatic relay 76 isprovided which, in the embodiment of FIGURE 4 is made an integral partof the housing means 202 immediately beneath the throttling valve bore206.

Referring to FIGURES 4, 6, 7 and 9, the relay 76 is shown as including apilot or signal chamber 74 connected on one side with a main air supplychamber 78 via a bleed port 80 having an in-line flow restrictor 82there- The main air chamber 78 is supplied via a supply port SP from asuitable source of supply pressure, not shown, and is connected with theoutput or branch pressure chamber 86 of the relay 76, by the upper halfof a two-way relay poppet 88 seating internally of the main air chamber78.

The lower end of the poppet 88 seats within the output chamber 86 on adiaphragm carried floating valve seat 90, whereby the output chamber 86is controllably interconnected with the exhaust chamber 92. The valveseat 90 is a part of a spacer structure 94 which separates and remainsmobile with the two diaphragms 96 and 98 which, combined with theinternal cavity of the relay 76, define the pilot, output and exhaustchambers 74, 86 and 92 respectively.

The exhaust chamber 92 is connected with the atmosphere via a vent port100. The branch pressure is de livered from the output chamber 86 to thethrottling valve bore 206 via a pressure port BPI.

The pilot pressure chamber 74 is connected via a pressure port PPl tothe journalled portion of the supporting shaft 222 of the positioningdisk assembly 210. The said shaft 222 includes a connecting pressureport PP2 which extends from the O-ring journal bearing and seal 224,through the positioning disk 216 to thereby connect the leakport 220 inthe leakport nozzle 218 with the pilot pressure chamber 92.

The back pressure developed by the leakport 220 and the leakport lever248 is manually adjustable via a calibrated control dial 268 which isfixed on the outer end of the supporting shaft 222 by an axial set screw270. The leakport lever 248 is adapted to engage the stop means 208 onthe throttling valve spindle 204 and thus, through the action of thetorsion spring 252, is constrained against same while the leakportnozzle 218 is moved relative to the leakport lever 248 via thecalibrated dial 268.

The throttling valve spindle 204 is provided with second and thirdradially disposed axially spaced branch pressure ports BP2 and BP3,respectively, the former providing communication between a pair of theO-ring seals 234, of the spindle cavity 232 with the branch pressurechamber 86 via the branch pressure port BP1. The third port BP3 providescommunication between another pair of the O-ring seals 234, of thespindle cavity 232 with a branch pressure output port BP4 which extendsto the exterior of the housing means 202.

The second branch pressure port BP2 in the valve spindle 204 is acylindrical bore which cooperates with the throttling valve head 228 toeffect a variable throttling of the branch pressure output of thepneumatic relay 76 as will be hereinafter described in more detail.

As shown in FIGURE 6, the angled cutting of the end surface 228 of thevalve head 226 provides a spherical silhouette overlying part of thearea of the second branch pressure port BP2, whereby either relativerotation or axial translation between the valve spindle 204 and thevalve head 226 will effect a variable throttling action on the branchpressure flow from the branch pressure chamber 86 to the output portBP4.

The assembly of FIGURE 4 is completed by electric leads P and Pconnected, respectively, to the servo motor 24 andthe transducer means266 which, if so desired may be combined in a single cable sheath P3extending through a Wiring access port 272 in the housing means 202.

In operation, referring to FIGURES 4 through 9, supply pressure has beenintroduced to the supply chamber 78 via the supply port SP therebyenergizing the pneumaticrelay 76.

Assuming an initial equilibrium condition, the servo motor 24 is thenenergized via the lead P and is rotated either clockwise orcounterclockwise depending upon the signal.

The rotation of the servo motor 24 is imparted to its shaft 40, piniongear 140, pinion gear 214 in the positioning disk assembly andconsequently, the leakport nozzle 218 and the leakport 220 on thepositioning disk 216 displaced With respect to the leakport lever 248which is constrained by the stop means 208 on the throttling valvespindle 204.

This results in a change in the back pressure reflected in the pilotchamber 74 by the leakport 220 and the differential pressure across thediaphragms 96 and 98 causes a corresponding unseating of one end or theother of the relay poppet 88 to counteract the pressure deviation in thepilot chamber 74 and tend to restore the relay 76 to a state ofequilibrium.

As a result of the action of the relay, the branch pressure must bevaried in the output chamber 86 to compensate for the pressure variationin the pilot chamber 74 and, as shown in and described with respect toFIGURE 3, this pressure change is imposed on the top work of thecontrolled valve shaft 104. In the embodiment of FIG- URES 4 and 9,however, the top Work 178 is connected with branch pressure from therelay 74 via the output port BP4.

Vertical displacement of the valve stem 104 in response to branchpressure changes results in rotation of the feedback pinions 116 and 118and the feedback shaft 120 via integral extension 108, chain 110, drum112 and shaft 114. This causes rotation of the throttling valve spindle204.

Simultaneously, the leakport lever 248 is constrained, by the stop means208 on the valve spindle 204, to be displaced toward a position ofequilibrium with respect to the leakport 220 and thereby rebalance thesystem. At the point of balance, the valve stem 104 has been moved to acontrolled position which satisfies the input constraint placed on thesystem by the input signal to the servo motor 24.

Since both the servo motor 24 and the pneumatic relay 76 have a rapidresponse to their respective input conditions, there are some largesignal swing applications in which overcontrol or hunting becomes aproblem.

This is overcome by rotating the throttling screw 244 to cause relativeaxial displacement between the second branch pressure port BP2 in thethrottling valve spool 204 and the throttling v-alve head 226. Thus, abranch pressure fiow can be selected which provides the proper signalresponse rate for optimum operation of the system.

During the entire control cycle, motion-to-signal transducer 266 isbeing rotated and transmits, via the lead P an electric signal which isa continuous function of the position of the valve stem 104.

The torsion spring 252 has a threefold function in that it maintains aconstraint on the leakport lever 248 to follow the leakport, maintainsthe positioning assembly pinion 214 under constant torque with thepinion gear to eliminate backlash and provides torque to the first andsecond feedback pinions 116 and 118, respectively, to effect a rewindingof the chain 110 on the drum 112 if in the event of an upwarddisplacement of the valve stem 104 as shown in FIGURE 4.

The drum 112 is utilized for the chain 110 when the valve stem 104 leadsto a controlled means having a straight line response. Suitable camshaped rewind means may be substituted for the drum 112 in the event ofa non-linear response characteristic in the controlled means.

Thus, as described above, this invention provides a novelcomputer-coordinated process control wherein a process parameter issensed by the computer and converted to a duration modulated binary orother multistate output signal; the computer output signal isselectively coupled, according to its state to the input terminals of abi-directional or multi-directional servo motor, respectively; theservomotor produces a directional output displacement proportional tothe duration of the input signal state and in a direction determined bythe said signal state and imposes a functionally related displacement ona leakport away from its associated leakport lever via suitable controlmeans; the leakport displacement causes a functionally related pilotpressure variation in a control relay means which produces a branchpressure output functionally related to the change in pilot pressure;the branch pressure variation causes a repositioning, via a fluid orpneumatic motor means, of a displaceable controller element such as aprocess control valve stem; the controller element causes a functionallyrelated displacement to be imparted to the leakport lever, via afeedback means, whereby the leakport lever is constrained to follow theleakport at a rate determined by the rate of displacement of thecontroller element and continuously modulate the pilot pressure untilthe change in pilot pressure has been overcome, whereby the relay willbe balanced and the controller element will be stopped after adisplacement determined by the duration modulated signal and thevariation in the process parameter sensed by the computer will becorrected.

.It is to be understood that the various embodiments of the inventionshown and described herein are for the purpose of example only and isnot intended to limit the scope of the appended claims.

What is claimed is:

1. A process control means for controlling process parameters comprisinginput means for sensing a variation in a process parameter and producinga durationmodulated multiple state electric signal in response thereto,electro-pneumatic converter means for producing a pneumatic pressurechange having a predetermined functional relationship with said electricsignal, displaceable controller means actuated by said pneumaticpressure from a first position through a displacement determined by saidpneumatic pressure change, and feedback means interconnecting saidcontroller means and said converter means, said feedback means acting onsaid converter means to continuously modulate said converter means inresponse to the displacement of said controller means until the effectof said pressure change on said controller means is equalized, wherebysaid controller means will stop in a second position; and meanscomprising transducer means driven by said feedback means producing anoutput signal as a .continuous function of the position of saiddisplaceable controller means; wherein said electro-pneumatic convertercomprises multi-directional electric servo motor means having motoroutput means actuated through a predetermined displacement and in adirection determined by the duration and state, respectively, of saidduration-modulated multiple-state electric signal, a pneumatic relayhaving a branch pressure. chamber and a pilot chamber with a constantsource of pressure supplied thereto, .a variable bleed means connectedwith said pilot chamber to variably exhaust pressure therefrom andcontrol the pilot pressure therein, first control means for saidvariable bleed means driven by said motor output means for varying thebleed rate thereof in response to said duration-modulated multiple-statesignal, whereby said pilot pressure is varied causing said relay to varythe branch pressure in said branch pressure chamber; a second controlmeans for said variable bleed means and resilient means interconnectingsaid first and second control means and biasing said second controlmeans to counteract said first control means, said displaceablecontroller means including pneumatic motor means actuated in response tosaid branch pressure and a displaceable means adapted to be displaced bysaid pneumatic motor means; and said feedback means comprises drivemeans interconnecting said displaceable means and said second controlmeans, said drive means acting to constrain said second control means inaccordance with the rate of displacement of said displaceable means,whereby the effect of said first control means on said variablebleedmeans is continually modulated during displacement of said displaceablemeans.

2. The invention defined in claim 1, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; saidsecond control means comprises a leakport lever extending radially fromthe axis of said torsion means at one end to a position adjacent saidleakport intermediate its ends and a second rotary control assemblyengaging said leakport lever intermediate its ends for constraining saidleakport lever with respect to said leakport against the action of saidtorsion means; and said feedback means comprises a gear train, first andsecond shaft means interconnected with said first shaft means, elongatedflexible means wound on said drum at one end thereof and connected withsaid displaceable means at the other end, said second shaft means beingaxially connected with said second rotary control assembly.

3. In a process control system including computer means for sensingvariations in process parameters and generating multiple-stateduration-modulated electric signals in response thereto and furtherincluding a displaceable controller means for controlling saidparameters, said controller being displaced by a pneumatic motor means,the invention comprising electro-pneumatic converter means for producinga branch pressure for actuating said pneumatic motor means and saidcontroller means to produce a displacement of said controller meanshaving a magnitude and direction determined by the duration and state,respectively, of said electric signals, said converter means comprisingmulti-directional electric servo motor means having motor output meansactuated through a predetermined displacement and in a directiondetermined by the said duration and state, respectively, of saidelectric signal, a pneumatic relay having a branch pressure chamber anda pilot chamber with a constant source of pressure supplied thereto, avariable bleed means connected with said pilot chamber to variablyexhaust pressure therefrom and control the pilot pressure therein, firstcontrol means for said variable bleed means driven by said motor outputmeans for varying the bleed rate thereof in response to said electricsignal, whereby said pilot pressure is varied causing said relay to varythe branch pressure in said branch pressure chamber, a second controlmeans for said variable bleed means and resilient means interconnectingsaid first and second control means and biasing said second controlmeans to counteract said first control means and throttling meansintegral with said control means selectively throttling the flow ofbranch pressure from said pneumatic relay to said pneumatic motor means.

4. The invention defined in claim 3, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; andsaid second control means comprises a leakport lever extending radiallyfrom the axis of rotation of said torsion means at one end to a positionadjacent said leakport intermediate its ends and a second rotary controlassembly engaging said leakport lever intermediate its ends forconstraining said leakport lever with respect to said leakport againstthe action of said torsion means, said second rotary control assemblybeing driven in response to a displacement of said displaceablecontroller means.

5. The invention defined in claim 3, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; andsaid second control means comprises a leakport lever extending radiallyfrom the axis of rotation of said torsion means at one end to a positionadjacent said leakport intermediate its ends and a second rotary controlassembly engaging said leakport lever intermediate its ends forconstraining said leakport lever with respect to said leakport againstthe action of said torsion means, said second rotary control assemblybeing driven in re- 'sponse to a displacement of said displaceablecontroller means; and further wherein said throttling means comprises avalve spool having port means interconnecting said branch pressurechamber and said pneumatic motor means coaxially integral with saidsecond rotary control assembly, set means selectively displacing saidvalve spool along said axis of rotation of said second assembly andvalve means coaxially. integral with said first rotary control assemblyengaging said valve spool and throttling said port means in an amountdetermined by said set means.

6. A process control means for controlling process parameters comprisinginput means for sensing a variation in a process parameter and producinga durationmodulated multiple state electric signal in response thereto,electro-pneumatic converter means for producing a pneumatic pressurechange having a predetermined functional relationship with said electricsignal, displaceable controller means actuated by said pneumaticpressure from a first position through a displacement determined by saidpneumatic pressure change, and feedback means interconnecting saidcontroller means and said converter means, said feedback means acting onsaid converter means to continuously modulate said converter means inresponse to the displacement of said controller means until the effectof said pressure change on said controller means is equalized, wherebysaid controller means will stop in a second position; and throttlingmeans, interconnected with said converter means and said controllermeans, selectively throttling flow occasioned by said pressure changebetween said converter means and said controller means, therebyproviding a selectively variable rate of response of said motor means tosaid durationmodulated electric signals.-

7. The invention defined in claim 6, wherein said electro-pneumaticconverter comprises multi-directional electric servo motor means havingmotor output means actuated through a predetermined displacement and ina direction determined by the duration and state, respectively, of saidduration-modulated multiple-state electricsignal, a pneumatic relayhaving a branch pressure chamber and apilot chamber with a constantsource of pressure supplied thereto, a variable bleed means connectedwith said pilot chamber to variably exhaust pressure therefrom andcontrol the pilot pressure therein, first control means for saidvariable bleed means driven by said motor output means for varying thebleed rate thereof in response to said duration-modulated multiple-statesignal, whereby said pilot pressure is varied causing said relay to varythe branch pressure in said branch pressure chamber; a second cont-r01means for said variable bleed means and resilient means interconnectingsaid first and second control means and biasing said second controlmeans to counteract said first control means, said displaceablecontroller means including pneumatic motor means actuated in response tosaid branch pressure and a displaceable means adapted to be displaced bysaid pneumatic motor means; and said feedback means comprises drivemeans interconnecting said displaceable means and said second controlmeans, said drive means acting to constrain said second control means inaccordance with the rate of displacement of said displaceable means,whereby the effect of said first control means on said variable bleedmeans is continually modulated during displacement of said displaceablemeans.

8. The invention defined in claim 7, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; saidsecond control means comp-rises a leakport lever extending radially fromthe axis of said torsion means at one end to a position adjacent saidleakport intermediate its ends and a second rotary control assemblyengaging said leakport lever intermediate its ends for constraining saidleakport lever with respect to said leakport against the action of saidtorsion means; and said feedback means comprises a gear train, first andsecond shaft means interconnected with said first shaft means, elongatedflexible means .wound on said drum at one end thereof and connected withsaid displaceable means at the other end, said second shaft means beingaxially connected with saidsecond rotary control assembly.

9. In a process control system including computer means for sensingvariations in process parameters and generating multiple-stateduration-modulated electric signals in response thereto and furtherincluding a displaceable controller means for controlling saidparameters, said controller being displaced by a pneumatic motor means,the invention comprising the combination of electro-pneumatic convertermeans for producing a branch pressure for actuating said pneumatic motormeans and said controller means to produce a displacement of saidcontroller means having a magnitude and direction determined by theduration and state, respectively, of said electric signals, and feedbackmeans interconnecting said controller means and said electric-pneumaticconverter means, said feedback means acting on said converter means tocontinuously modulate said converter means until the effect of saidpressure change on said controller means is equalized; said convertermeans including means selectively varying the rate of response of saidpneumatic motor means to said electric signals comprising variablethrottling means providing selective adjustment of branch pressure flowbetween said converter means and said pneumatic motor means.

10. The invention defined in claim 9, wherein said converter meanscomprises multi-directional electricservo motor means having motoroutput means actuated through a predetermined displacement and in adirection determined by the said duration and state, respectively, ofsaid electric signal, a pneumatic relay having a branch pressure chamberand a pilot chamber with a constant source of pressure supplied thereto,a variable bleed means connected with said pilot chamber to variablyexhaust pressure therefrom and control the pilot pressure therein, firstcontrol means for said variable bleed means driven by said motor outputmeans for varying the bleed rate thereof in response to said electricsignal, whereby said pilot pressure is varied causing said relay to varythe branch pressure in said branch pressure chamber, a second controlmeans for said variable bleed means and resilient means interconnectingsaid first and second control means and biasing said second controlmeans to counteract said first control means; and said feedback meanscomprises drive means interconnecting said displaoeable controller meansand said second control means, said drive means acting to constrain saidsecond control means in accordance with the rate of displacement of saiddisplaceable controller means, whereby the effect of said first controlmeans on said variable bleed means is continually modulated duringdisplacement of said displaceable controller means.

11. The invention defined in claim 10, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; saidsecond control means comprises a leakport lever extending radially fromthe axis of said torsion means at one end to a position adjacent saidleakpo-rt intermediate its ends and a second rotary control assemblyengaging said leakport lever intermediate its ends for constraining saidleakport lever with respect to said leakport against the action of saidtorsion means; and said drive means of said feedback means comprises agear train, first and second shaft means interconnected through saidgear train, a drum axially connected with said first shaft means,elongated flexible means wound on said drum at one end thereof andconnected with said displaceable controller means at the other end, saidsecond shaft means being axially connected with said second rotarycontrol assembly.

12. The invention defined in claim 9, wherein said converter meanscomprises multi-directional electric servomotor means having motoroutput means actuated through a predetermined displacement and in adirection determined by the said duration and state, respectively, ofsaid electric signal, a pneumatic relay having a branch pressure chamberand a pilot chamber with a constant source of pressure supplied thereto,a variable bleed means connected with said pilot chamber to variablyexhaust pressure therefrom and control the pilot pressure therein, firstcontrol means for said variable bleed means driven by said motor outputmeans for varying the bleed rate thereof in response to said electricsign-a1, whereby said pilot pressure is varied causing said relay tovary the branch pressure in said branch pressure chamber, a secondcontrol means for said variable bleed means and resilient meansinterconnecting said first and second control means and biasing saidsecond control means to counteract said first control means; and saidfeedback means comprises drive means interconnecting said displaceablecontroller means and said second control means, said drive means actingto contrain said second control means in accordance 'with the rate ofdisplacement of said displaceable controller means, whereby the effectof said first control means on said variable bleed means is continuallymodulated during displacement of said displaceable controller means; andfurther wherein said throttling means comprises variable valve meansintegral with both said first and second control means.

13. The invention defined in claim 12, wherein said motor output meanscomprises a rotary shaft; said variable bleed means comprises aleakport; said first control means comprises a first rotary controlassembly driven by said motor shaft and support means on said assemblyretaining said leakport on said assembly radially of the axis ofrotation thereof; said resilient means comprises a torsion means; saidsecond control means comprises a leakport lever extending radially fromthe axis of said torsion means at one end to a position adjacent saidleakport intermediate its ends and a second rotary control assemblyengaging said leakport lever intermediate its ends for constraining saidleakport lever with respect to said leakport against the action of saidtorsion means; and said drive means of said feedback means comprises agear train, first and second shaft means interconnected through saidgear train, a drum axially connected with said first shaft means,elongated flexible means wound on said drum at one end thereof andconnected with said displaceable controller means at the other end, saidsecond shaft means being axially connected with said second rotarycontrol assembly; and further wherein said variable valve meanscomprises a valve spool integral and coaxial with said second shaftmeans, set means providing selective axial displacement of said secondshaft means and said valve spool with respect to said first controlassembly, port means in said valve spool interconnecting said branchpressure chamber and said displaceable controller means and valve headmeans coaxial with said first control assembly engaging said valve spooland throttling said port means in an amount determined by said setmeans.

References Cited by the Examiner UNITED STATES PATENTS 2,789,543 4/1957Popowsky 91-387 2,985,808 12/ 1959 Ketchledge 3 10-20.209 3,03 8,4496/1963 Murphy et al 9l-363 3,040,715 6/1963 McCombs et a1. 91-3823,101,031 8/1963 Crossley 91-387 3,160,836 12/1964 Farley .L 925 EDGARW. GEOG-I-IEGAN, Primary Examiner. SAMUEL LEVINE, Examiner. P. E.MASLOUSKY, Assistant Examiner,

1. A PROCESS CONTROL MEANS FOR CONTROLLING PROCESS PARAMETERS COMPRISINGINPUT MEANS FOR SENSING A VARIATION IN A PROCESS PARAMETER AND PRODUCINGA DURATIONMODUALTED MUTLIPLE STATE ELECTRIC SIGNAL IN RESPONSE THERETO,ELECTRO-PNEUMATIC CONVERTER MEANS FOR PRODUCING A PNEUMATIC PRESSURECHANGE HAVING A PREDETERMINED FUNCTIONAL RELATIONSHIP WITH SAID ELECTRICSIGNAL, DISPLACEABLE CONTROLLER MEANS ACTUATED BY SAID PNEUMATICPRESSURE FROM A FIRST POSITION THROUGH A DISPLACEMENT DETERMINED BY SAIDPNEUMATIC PRESSURE CHANGE, AND FEEDBACK MEANS INTERCONNECTING SAIDCONTROLLER MEANS AND SAID CONVERTER MEANS, SAID FEEDBACK MEANS ACTING ONSAID CONVERTER MEANS TO CONTINUOUSLY MODULATE SAID CONVERTER MEANS INRESPONSE TO THE DISPLACEMENT OF SAID CONTROLLER MEANS UNTIL THE EFFECTOF SAID PRESSURE CHANGE ON SAID CONTROLLER MEANS IS EQUALIZED, WHEREBYSAID CONTROLLER MEANS WILL STOP IN A SECOND POSITION; AND MEANSCOMPRISING TRANSDUCER MEANS DRIVEN BY SAID FEEDBACK MEANS PRODUCING ANOUTPUT SIGNAL ASA A CONTINUOUS FUNCTION OF THE POSITION OF SAIDDISPLACEABLE CONTROLLER MEANS; WHEREIN SAID ELECTRO-PNEUMATIC CONVERTERCOMPRISES MULTI-DIRECTIONAL ELECTRIC SERVO MOTOR MEANS HAVING MOTOROUTPUT MEANS ACTUATED THROUGH A PREDETERMINED DISPLACEMENT AND IN ADIRECTION DETERMINED BY THE DURATION AND STATE, RESPECTIVELY, OF SAIDDURATION-MODULATED MULTIPLE-STATE ELECTRIC SIGNAL, A PNEUMATIC RELAYHAVING A BRANCH PRESSURE CHAMBER AND A PILOT CHAMBER WITH A CONSTANTSOURCE OF PRESSURE SUPPLIED THERETO, A VARIABLE BLEED MEANS CONNECTEDWITH SAID PILOT CHAMBER TO VARIABLY EXHAUST PRESSURE THEREFROM ANDCONTROL THE PILOT PRESSURE THEREIN, FIRST CONTROL MEANS FOR SAIDVARIABLE BLEED MEANS DRIVEN BY SAID MOTOR OUT-